The blues has deep roots in American history, particularly African-American history. The blues originated on Southern plantations in the 19th Century. Its inventors were slaves, ex-slaves and the descendants of slaves—African-American sharecroppers who sang as they toiled in the cotton and vegetable fields. It's generally accepted that the music evolved from African spirituals, African chants, work songs, field hollers, rural fife and drum music, revivalist hymns, and country dance music.
The blues grew up in the Mississippi Delta just upriver from New Orleans, the birthplace of jazz. Blues and jazz have always influenced each other, and they still interact in countless ways today.
Unlike jazz, the blues didn't spread out significantly from the South to the Midwest until the 1930s and '40s. Once the Delta blues made their way up the Mississippi to urban areas, the music evolved into electrified Chicago blues, other regional blues styles, and various jazz-blues hybrids. A decade or so later the blues gave birth to rhythm 'n blues and rock 'n roll.